Chapter001


Chapter 1

Cell Structure and Function

Chapter 1

Cell Structure and Function


Cell StructureCell Structure


Cell ComponentsCell Components

• Nucleus and nucleolus• Cytoplasm and cytoplasmic organelles

– Ribosomes– Endoplasmic reticulum– Golgi complex– Lysosomes, peroxisomes– Mitochondria

• Cytoskeleton– Microtubules, microfilaments


The Plasma MembraneThe Plasma Membrane


Red Blood Cells Start Out with All the OrganellesRed Blood Cells Start Out with All the Organelles

• As they mature, they:

– Lose their lysosomes

– Produce hemoglobin

– Have small Golgi bodies

– Have enlarged endoplasmic reticulum

• When they are mature, they:

– Lose their endoplasmic reticulum

– Lose their mitochondria

How does this relate to their function?How does this relate to their function?


QuestionQuestion

By the time a red blood cell (RBC) is mature, it has lost all but which of the following?

a. lysosomes

b. endoplasmic reticulum

c. hemoglobin

d. mitochondria


AnswerAnswer

c. hemoglobin

Because the function of the RBC is to carry oxygen, hemoglobin is an essential component of the cell (each hemoglobin molecule can carry four molecules of oxygen) . Lysosomes, endoplasmic reticulum, and mitochondria all exert some metabolic function in other cells. But, if they remained in the RBC, the oxygen on board would be consumed before reaching its destination.


Cell Metabolism and Energy SourcesCell Metabolism and Energy Sources


Anaerobic Energy Metabolism—GlycolysisAnaerobic Energy Metabolism—Glycolysis

• In the cytoplasm, molecules are broken into 2-carbon chunks

– Glycolysis breaks sugar 2 ATP molecules formed

– Other pathways break fatty acids or amino acids

– Breaking molecules involves removing electrons

º Handed to electron carriers like NAD and FAD

º H+ follows the electrons

– Afterwards, they are put back on the 2-carbon chunks

º Forming lactic acid


Aerobic Energy Metabolism—Krebs CycleAerobic Energy Metabolism—Krebs Cycle

• 2-carbon molecules enter the mitochondrion matrix space

– Krebs cycle breaks them down 1 ATP molecule formed

– Carbon is lost as CO2


Krebs Cycle Occurs within MitochondriaKrebs Cycle Occurs within Mitochondria

• Breaking molecules involves removing electrons

– Handed to electron carriers like NAD and FAD

– H+ follows the electrons

– Many of these electron carriers are loaded up with electrons by the Krebs cycle


QuestionQuestion

Tell whether the following statement is true or false:

ATP is produced in the mitochondria.


AnswerAnswer

True

The Krebs cycle occurs in the mitochondria. Each Krebs cycle produces one molecule of ATP.


Diffusion Is Movement of MoleculesDiffusion Is Movement of Molecules

• Passive diffusion: molecules move randomly away from the area where they are most concentrated

• Facilitated diffusion: molecules diffuse across a membrane by passing through a protein

• Osmosis: diffusion of water molecules


QuestionQuestion

Your patient has been given an intravenous solution of water. What will happen to this patient’s red blood cells?

a. They will burst/lyse.

b. They will shrink.

c. They will not be affected by the water solution.


AnswerAnswer

a. They will burst/lyse.

Osmosis causes movement from “more watery” to “less watery.” Because water is “more watery” than the RBC (it’s water, after all), water moves into the cell, causing it to expand and burst/lyse.


Cell CommunicationCell Communication

• A messenger molecule attaches to receptor proteins on cell surface

• Receptor proteins cause cell to respond by:

– Opening ion channels to let ions in or out

– Causing a second molecule to be released inside the cell

– Turning on enzymes inside the cell

– Stimulating the transcription of genes in the nucleus


The Basics of Cell FiringThe Basics of Cell Firing

• Cells begin with a negative charge: resting membrane potential

• Stimulus causes some Na+ channels to open

• Na+ diffuses in, making the cell more positive


The Basics of Cell Firing (cont.)The Basics of Cell Firing (cont.)

• At threshold potential, more Na+ channels open

• Na+ rushes in, making the cell very positive: depolarization

• Action potential: the cell responds (e.g., by contracting)


The Basics of Cell Firing (cont.)The Basics of Cell Firing (cont.)

• K+ channels open

• K+ diffuses out, making the cell negative again: repolarization

• Na+/K+ ATPase removes the Na+ from the cell and pumps the K+ back in


QuestionQuestion

Tell whether the following statement is true or false:

An action potential is the result of K+ movement out of the cell.


AnswerAnswer

False

An action potential occurs when Na+ moves into the cell, making it more positive on the inside (depolarization). When K+ leaves the cell, it becomes less positive (more negative) until it returns to resting membrane potential (repolarization).


Na+ enters cell and muscle cell

depolarizes

Ca2+ released from sarcoplasmic reticulum into the

sarcoplasm

Ca2+ attaches to

troponin


QuestionQuestion

What happens to the sarcomere when myosin slides across the actin binding sites?

a. It gets longer.

b. It gets shorter.

c. There is no change in length.

d. It releases acetylcholinesterase.


AnswerAnswer

a. It gets shorter.

When the myosin binds with exposed actin sites (myosin “reaches” forward like your hands do when pulling end-over-end on a rope), the Z lines get pulled closer together, and the muscle cell shortens/contracts.

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